An Electrochemically Reconstructed Ternary Heterostructure for Efficient Ammonia Production in an Asymmetric Seawater‐Based Electrosynthesis Reactor

Coupling the nitrate reduction reaction (NO 3 − RR) with seawater‐based electrosynthesis systems provides a sustainable way for simultaneous ammonia (NH 3 ) production and active chlorine (AC), yet practical implementation remains limited by the complex multielectron‐proton coupling of NO 3 − RR. Herein, we develop a cobalt‐copper doped W 2 N 3 (CoCu‐W 2 N 3 ) precatalyst that can be electrochemically reconstructed into a Cu 0/1+ ‐Co(OH) 2 ‐W 2 N 3 ternary heterostructure with enhanced NO 3 − RR performance. This ternary heterostructure enables coordinated deoxygenation, intermediates transfer, and hydrogenation throughout the NO 3 − RR process. As a result, the catalyst achieves an NH 3 Faradaic efficiency (FE) of over 96% and maintains stable operation for 348 h. To enhance its practical applicability, we designed a seawater‐based bipolar‐membrane system coupling NO 3 − RR with AC generation. The system achieved an NH 3 Faradaic efficiency greater than 90% at 120 mA cm −2 while simultaneously producing a disinfectant suitable for medical environment applications. Techno‐economic analysis estimates that the cost of producing a kilogram of NH 3 using this system is US$2.37, with further cost reduction potential unlocked by pairing nitrate‐rich wastewater and surplus renewable energy.